Fixed and especially mobile-networks, such as Global System for Mobile communications (GSM), General Packet Radio System (GPRS) or Universal Mobile Telecommunication System (UMTS) are constantly evolving. GSM/GPRS and UMTS networks today offer both Circuit Switched (CS) connectivity and Packet Switched (PS) connectivity. The PS end-to-end connectivity with its capabilities for transmission of a wide range of data types may be used for offering multimedia services such as image, music and video transfer. The CS connectivity provides a link between two User Equipment by means of one or more trusted network-nodes with a reliable and defined Quality of Service (QoS) for e.g. voice traffic.
Combinational networks, where at least two links of at least two different network types e.g. CS or PS, to one or more User Equipment are established, are capable of deploying CS and PS connectivity simultaneously to a User Equipment, thereby enabling services, which perform their activity by PS-communication sessions, and CS communication sessions denoted as CS-calls. As this invention is presented with application of an Internet Protocol Multimedia Subsystem (IMS) service, executed as a PS-communication session, the remainder of the invention denotes the PS_communication session as an IMS-session.
As to benefit from this form of service combination, User Equipment comprising one or more terminals are required that are capable of handling a CS-call and an IMS-session simultaneously. Multi Radio Access Bearer (RAB) terminals for UMTS and Dual Transfer Mode (DTM) terminals for GSM/GPRS networks will be available; these types of terminals provide support for simultaneous CS- and PS-connectivity.
Today, conversational voice cannot be delivered over PS radio bearers to the end-user, due to e.g. insufficient capacity in the Radio Access Networks in operation and therefore existing CS bearers are used for delivering conversational voice. In the future, it may be possible that a single PS bearer is used for conversational voice and multimedia. Nevertheless, DTM terminals already—, and possibly UMTS terminals in the future, deliver support for simultaneous CS- and PS-connectivity.
In order to give the end-user the look and feel of a single service, although the service may be composed of various CS-calls and IMS-sessions, deployed in the CS-network and the PS-network respectively, it is desirable to determine and deploy some form of relation between ongoing CS-calls or CS-calls that are being established and the ongoing IMS-session(s) or IMS-session(s) that are being established. In the case that a CS-call is terminated or temporarily suspended, the related IMS-session(s) should be terminated or suspended as well as to provide the user the perception that both communication sessions are strictly related to each other and provide a combined service.
A Call Hold event is an example of an event in a CS-network that may have effect in a simultaneous and correlated IMS-session at a User Equipment. Call Hold is an example of a supplementary service in the context of Combinational Services, i.e. CS-services complemented with IMS, as defined by 3.rd Generation Partnership Project (3GPP), services, e.g. 3GPP specification TS 22.083, Call Waiting and Call Hold.
Although deploying telecommunication services such as voice, video and data, over PS networks seems to be a realistic scenario for the near future, some state of the art wireless networks e.g. GSM or UMTS, would not be able to provide the required Quality of Service (QoS) for voice traffic over a radio bearer of a PS network.
Combinational services, where the voice services are transported via the traditional CS network and the video and data services via the PS-network provide a solution with respect to referred QoS.
The CS-networks provide a number of CS-services, e.g. supplementary services, for CS-calls. Currently developed IMS applications provide a number of IMS-services for IMS-sessions available to an end-user via the PS-networks.
When an IMS service is applied within a combinational network, where the CS-call is transported via the CS-network and the IMS-sessions are transported via the PS-network, there is no relation between the CS-call provided by the CS-service and IMS session provided by the IMS-service, as the CS-call and the IMS-session are unrelated to each other due to transportation via different bearers.
3GPP specifications TS 22.083 [Call Waiting and Call Hold supplementary services, stage 1], TS 23.083 [Call Waiting and Call Hold supplementary services, stage 2], TS 24.080 [Mobile radio Layer 3 supplementary service specification; formats and coding], and TS 24.083 [Call Waiting and Call Hold supplementary services, stage 3] describe in detail a CS service Call Waiting and Call Hold. The Call Hold service allows a served mobile subscriber, who is provisioned with this Supplementary Service (SS), to interrupt communication on an existing active CS-call and subsequently, if desired, re-establish communication. A traffic channel remains assigned to the mobile subscriber after the communication is interrupted to allow the origination or termination of other calls [according to TS 22.083 stage 1].
When a Call Hold service is invoked, communication is interrupted on the traffic channel and the traffic channel is released from the existing call. The traffic channel is reserved for the served mobile subscriber invoking the Call Hold service. The served mobile subscriber has one call on hold at a time.
One traffic channel should be reserved for the served mobile subscriber as long as the subscriber has one call on hold and is currently not connected to any other call, i.e. the network should not reserve more than one traffic channel for a mobile station.
If the served mobile subscriber has a call on hold and is not connected to an active call, the subscriber either: retrieves the held call, sets up another call, or disconnects the held call.
If the served mobile subscriber has a call on hold and is not connected to an active call, the subscriber cannot receive a call, except when using the Call Waiting Supplementary Service.
If the served mobile subscriber is connected to an active call and has another call on hold, the subscriber either: alternates from one call to the other, disconnects the active call, or disconnects the held call, or disconnects both calls. If the served mobile subscriber is connected to an active call and has another call on hold, the subscriber cannot receive a call. More detailed information is comprised in 3GPP TS 22.083.
The Call Hold Supplementary Service has been specified within a CS context. At the moment of specifying this Call Hold service, there were no IMS services specified and therefore not included.
During the specification of IMS protocols and architecture it was assumed that the voice component of multimedia services would be using conversational PS-network bearers. Operator defined IMS-services may be executed by a Service Network. These IMS-services are not specified by IMS. Within IMS a number of primitives are specified which enable the Service Network to execute IMS services. There is no existence of an “IMS-session Hold service” defined within the IMS specifications in analogy towards the Call Hold service within the CS-domain.
Considering the deployment of a CS-domain service in combination with a PS-service such as IMS services, i.e. Combinational Services, a new area of service interaction between CS-domain and IMS-domain based IMS services occurred. For the combined Call Hold service, both the CS-domain service and the IMS services need to be suspended and the CS-domain- and IMS connectivity interrupted, when a Call Hold event has occurred within the CS-network.
An additional issue is the influence of the security principles within the network. In general a User Equipment is not regarded as a trusted entity within the network, although it is responsible for the initiation of a number of relevant network procedures, such as Call Hold. Therefore, a validation mechanism needs to be available that complements the User Equipment as to compensate the “untrusted” nature of the User Equipment.